<PAGE>
 
                                                                  EXHIBIT 10.23



                             SERVICE AGREEMENT

         This Service  Agreement (the "Agreement") is made and entered into
this 6th day of November 1998, by and between COMSAT Mobile Communications,
a business unit of COMSAT Corporation, a corporation organized and existing
under the laws of the  District of Columbia,  with offices  located at 6560
Rock  Spring  Drive,   Bethesda,   Maryland  20871   ("COMSAT"),   and  MCI
International, Inc., a corporation organized and existing under the laws of
Delaware,  with offices at 2 International Drive, Rye Brook, New York 10573
("MCI").  COMSAT and MCI are  hereinafter  collectively  referred to as the
"Parties" and individually referred to as a "Party".

WHEREAS,  COMSAT provides mobile satellite  communications  services to and
from  mobile  earth  stations  via  the   International   Mobile  Satellite
Organization  ("Inmarsat")  satellite  system  through  COMSAT's land earth
stations and switching facilities; and

WHEREAS,  MCI  maintains  a  terrestrial   telecommunications  network  and
provides telecommunication  services,  including telex services, within the
United States and abroad; and

WHEREAS,  both Parties desire to obtain the services of the other Party and
are willing to interconnect  facilities for the purpose of facilitating the
mutual  provision of services in accordance  with the terms and  conditions
set forth herein.

NOW, THEREFORE,  in consideration of the foregoing and the mutual covenants
herein expressed, COMSAT and MCI agree as follows:

1.       DEFINITIONS

1.1      "COMSAT  Facilities"  shall mean land earth  stations  ("LES") and
         switching facilities provided by COMSAT.

1.2      "COMSAT  Services" shall mean Standard-A,  -M, -B, Mini-M and Aero
         mobile satellite  communication  services to and from mobile earth
         stations  via  the  Inmarsat   satellite   system  through  COMSAT
         Facilities.

1.3      "Effective Date" shall mean November 1, 1998.

1.4      "Fixed-to-Mobile  Traffic" shall mean U.S. traffic  originating on
         MCI  Facilities in a fixed location and destined to terminate at a
         mobile earth station via the Inmarsat satellite system.

1.5      "Inmarsat  Ocean  Regions"  shall mean the  Pacific  Ocean  Region
         ("POR"),  the Atlantic Ocean Region-West  ("AOR-W"),  the Atlantic
         Ocean Region-East ("AOR-E") and the Indian Ocean Region ("IOR").

1.6      "MCI Facilities" shall mean MCI's international  switching centers
         and other terrestrial facilities owned or controlled by MCI or, as
         the case may be, the  facilities  of any local  exchange  carriers
         selected by MCI for the  termination of  Mobile-to-Fixed  Traffic.
         MCI's Facilities shall not include facilites owned and operated by
         Worldcom,  Inc. or its affiliates prior to the merger of Worldcom,
         Inc. and MCI Communications Corporation.

1.7      "MCI Services" shall mean terrestrial  communications  services to
         and from  fixed  international  or  domestic  land  points via MCI
         Facilities.

1.8      "MES" shall mean mobile earth station.

1.9      "Mobile-to-Fixed  Traffic" shall mean traffic  originating  from a
         mobile  earth  station  via  the  Inmarsat  satellite  system  and
         COMSAT's   Facilities   and  destined  to  terminate  at  a  fixed
         international or domestic land point.

1.10     "Transit   Traffic"   shall  mean   traffic  to  an  Inmarsat  MES
         originating  from a  fixed  location  in a  country  in  which  no
         Inmarsat land earth station exists to provide  service to such MES
         and  which  traffic  is  routed  over  MCI  Facilities  to  COMSAT
         Facilities for delivery to its final destination.
<PAGE>
 
2.       TERM OF AGREEMENT.

         Unless  otherwise  terminated  pursuant to Article 7 hereof,  this
         Agreement shall be effective for a period of one year,  commencing
         on the Effective Date ("Initial Term").

3        SERVICE PROVISION AND RATES

3.1      COMSAT shall provide COMSAT Services to MCI at the rates set forth
         in  Attachment  A hereto in order to allow MCI to  terminate  U.S.
         originated Fixed-to-Mobile Traffic. Notwithstanding the foregoing,
         COMSAT  shall  provide a  discount  to its rates for  Standard  -A
         services  in  consideration  of MCI's  commitment  to program  its
         switches and undertake any other  measures  necessary to direct to
         COMSAT a minimum of  seventy-five  (75%) of MCI's  U.S.-originated
         Inmarsat  -A, -M,  -B,  Mini-M  and Aero  Fixed-to-Mobile  Traffic
         destined to the AOR-E,  AOR-W and POR. The discount  rate shall be
         as set forth in  Attachment  A. In order to receive the  discount,
         internal  monthly  reviews shall be conducted by COMSAT to measure
         actual  Fixed-to-Mobile  traffic  delivered by MCI to COMSAT.  The
         rates set forth in  Attachment  A shall be  inclusive of all space
         and ground segment charges. COMSAT shall be solely responsible for
         such charges and MCI shall have no responsibility therefor.

3.2      MCI shall  provide  MCI  Services  to  COMSAT  to allow  COMSAT to
         terminate  Mobile-to-Fixed  Traffic  at the  rates  set  forth  in
         Attachment B hereto.  COMSAT  shall be eligible  for  discounts as
         described  in  Attachment  B. The rates set forth in  Attachment B
         shall be inclusive of all  pay-outs and other  amounts  payable to
         any local, long distance or other carrier or administration and/or
         other operating  entities with respect to MCI Service  terminating
         in or transiting through their jurisdictions.  MCI shall be solely
         responsible for settlements with and payments to such carriers and
         COMSAT shall have no responsibility therefor.

3.3      The rates set forth in Attachments A and B shall be effective as of 
         November 1, 1998.

3.4      Transit Traffic

3.4.1    For Transit Traffic,  COMSAT will establish transit rates with the
         foreign  administrations  for the LES  component of the charge and
         MCI will establish the international land line charges.

3.4.2    For Transit Traffic where the foreign administration  accounts and
         settles with COMSAT for the LES component  ("Direct  Settlement"),
         the foreign telephone administration shall account and settle with
         MCI for the  international  land line  charges.  In the event that
         cascade accounting is utilized, MCI shall credit COMSAT the amount
         due COMSAT and  settlement  shall be in  accordance  with  Section
         6.1.2. MCI shall provide  sufficient  detail on a monthly basis to
         enable COMSAT to determine the foreign  administration  from which
         the call originated,  volume and ocean region  destinations of the
         Transit Traffic.

4.       INTERCONNECTION OF FACILITIES.

4.1      COMSAT and MCI agree to  interconnect  COMSAT  Facilities  and MCI
         Facilities   to  permit  the  exchange  of   Fixed-to-Mobile   and
         Mobile-to-Fixed  Traffic. The points of interconnections  shall be
         at COMSAT's Main Distribution Frame ("MDF") at COMSAT's Facilities
         at Santa Paula, California and Southbury, Connecticut.

4.2      Each Party shall be responsible for providing and maintaining,  at
         its own expense and liability,  the equipment and circuits located
         on its  side  of the  MDF.  The  Parties  shall  cooperate  in the
         detection and  correction of problems which can not be immediately
         isolated to a specific side of the MDF or segment of a circuit.

4.3      Except as otherwise agreed by the Parties, the technical standards
         and methods of operation applied by the Parties in the exchange of
         traffic hereunder shall conform to the applicable  recommendations
         of the International Telecommunications Union - Telecommunications
         Standardization Sector ("ITU-T") and to any revisions of same. The
         Parties agree that the  signaling  standard  shall  continue to be
         Signaling System
<PAGE>
 
         No. 5.  Such signaling standard may be upgraded to Signaling System 
         No. 7 upon availability and mutual agreement of the Parties.

5.       APPLICABLE SERVICE STANDARDS

5.1      COMSAT  Services.  COMSAT shall provide  COMSAT  Services  through
         COMSAT   Facilities   which   satisfy  the   applicable   Inmarsat
         specifications for such services.  COMSAT's failure to comply with
         non-mandatory specifications shall not be deemed to be in conflict
         with this Agreement.

5.2      MCI Services.  MCI shall provide services through its facilities 
         which satisfy ITU Recommendations Q. 140 through Q. 157 for Signaling 
         System No. 5.

6.       PAYMENT FOR SERVICE

6.1      Accounting and Settlement Procedures.

6.1.1    Each Party shall be responsible  for  establishing  end-user rates
         for services  rendered to its respective  customers.  In addition,
         each  Party  shall  be  responsible  to bill and  collect  service
         charges from its respective customers.

6.1.2    No later  than  sixty  (60) days after the end of a service
         month, the Parties shall exchange  accounting  statements for services
         provided to each other during the preceding calendar month. Each Party
         shall  provide  to the  other  Party  such  detail  as each  Party may
         reasonably require to determine the appropriate settlement between the
         Parties. At a minimum, the monthly statement shall contain the type of
         service,  the Inmarsat Ocean Region,  the number of calls, the minutes
         carried  and  the  rates  applicable  to  each  minute.  Such  monthly
         statement   shall  be   provided   via  a  printed   statement   until
         implementation of settlement disk processing. The Parties shall reduce
         to a net  balance  the sum due in U.S.  Dollars  each  month from each
         Party to the other Party.  Net  balances  due from one Party  ("Debtor
         Party") to the other  Party  ("Creditor  Party")  shall be paid by the
         Debtor Party to the Creditor  Party.  Settlement of net balances shall
         be made  within  forty-five  (45) days of receipt of invoice  from the
         Creditor Party. The inability of a Party to collect from its end users
         shall not relieve such Party's obligation to make payment to the other
         Party for services rendered hereunder.

6.2      Billing  Disputes.  Each Party is responsible  for the accuracy of
         any  accounting  statement or invoice that it submits to the other
         Party.  An  accounting  statement  shall be  deemed  to have  been
         accepted  by the Party to whom it is  rendered  if such Party does
         not  object  in  writing  thereto  before  the  end of the  second
         calendar  month  following  the  month in  which  the  account  is
         transmitted by the Party rendering it. Agreed adjustments shall be
         included in the following monthly accounting statement. Objections
         to an invoice that are not raised within twelve (12) months of the
         date on which an invoice is  received  by a Party  shall be deemed
         waived by such Party and such invoice shall be deemed final.

6.3.1    Taxes.  Each  Party  shall be  responsible  for its own tax or tax
         related  surcharges  determined by reference to income, net worth,
         franchise  or property  and any other tax imposed  directly on the
         Party.

6.3.2    With regard to services  originated  and billed to a purchaser  by
         MCI,  MCI  agrees  to  be  responsible   for  the   determination,
         collection and remittance of all appropriate taxes imposed thereon
         including but not limited to United States federal  excise,  state
         and local sales,  gross receipts and similar taxes. With regard to
         services  originated  and billed to a purchaser by COMSAT,  COMSAT
         agrees to be  responsible  for the  determination,  collection and
         remittance of all appropriate  taxes imposed thereon including but
         not  limited  to United  States  federal  excise,  state and local
         sales, gross receipts and similar taxes.

         In the event that an exemption  certificate  is required by either
         Party, all efforts will be made to provide such certificate to the
         requesting Party.
<PAGE>
 
7.       TERMINATION.

7.1      Termination  . This  Agreement  may be  terminated by either Party
         ("Terminating  Party") to the other Party (the "Defaulting Party")
         in the event that one (1) or more of the  following  events  shall
         occur and which  event(s)  shall not have been  cured  within  the
         thirty  (30) day period  from the date of written  notice  thereof
         from the Terminating Party to the Defaulting Party: (a) failure of
         the  Defaulting  Party  to  pay  any  sum  due  and  owing  to the
         Terminating Party within the payment period specified in Section 6
         hereof;  or (b)  failure of the  Defaulting  Party to perform  any
         material obligation contained in this Agreement.

7.1.1    Consequence  of  Termination.  Termination  or  expiration of this
         Agreement  in  accordance  with its terms  shall not  release  the
         Parties hereto from any liability which at the time of termination
         or expiration has already  accrued or which  thereafter may accrue
         in  respect  of any  act or  omission  of a  Party  prior  to such
         termination  or  expiration,  or  from  any  obligation  which  is
         expressly  stated in this  Agreement  to  survive  termination  or
         expiration.

7.1.2    Upon expiration or termination of this Agreement:

         a.       Neither Party shall be obligated to provide its services to 
                  the other Party;

         b.       Each  Party  shall  return or  destroy  all  Confidential
                  Information of the other Party in its possession no later
                  than five (5) business days following the  termination or
                  expiration date; and

         c.       All mutual  indebtedness  of the Parties  that shall have
                  accrued as of the date of termination or expiration shall
                  become due and payable within thirty (30) days thereof.

8.       LIABILITY; GENERAL INDEMNITY

8.1      In no event  shall  either  Party be liable to the other Party for
         any special,  indirect,  incidental,  punitive,  consequential  or
         exemplary  damages,  including without limitation loss of revenue,
         loss of profits, loss of clients or goodwill arising in any manner
         from this  Agreement  and the  performance  or  nonperformance  of
         business hereunder.

8.2      With respect to the service that each Party  provides to the other
         Party hereunder,  neither Party shall be liable for, and expressly
         disclaims any liability to the other Party, its customers, assigns
         or any other person or entity for any damages, claims,  liability,
         expenses,  or loss,  regardless of the degree of fault or failure,
         including  but not  limited to damage to  property  and claims for
         personal  injury  or death,  sustained  by the  other  Party,  its
         customers,  assigns  or any other  person or entity for any reason
         relating  to  the  unavailability,  delay,  outage,  interruption,
         disruption,  break-down,  degradation,  error in transmission,  or
         failure arising out of, relating to, or in any way associated with
         the  Services,   satellites,   land  earth  stations,   equipment,
         operations,  or facilities that are involved in the performance of
         this  Agreement,  regardless of the cause or causes  thereof,  and
         regardless of whether or not  attributable to any negligent act or
         omission or whether or not such act or omission constitutes,  with
         respect  to any  person  or  entity,  failure  to meet  any of its
         obligations.

8.3      With respect to the COMSAT Services provided hereunder, MCI agrees
         that  Inmarsat  shall  not be  liable  to the same  extent  as the
         disclaimers of liability in this Article.

8.4      Each Party agrees to include, in any contract,  agreement,  tariff
         or  other  undertaking  between  it and  any  customer  or  assign
         relating to the  services,  operations,  equipment  or  facilities
         involved in the performance of this Agreement, a provision stating
         that the  disclaimers  of liability as set forth above shall apply
         in full to said contract, agreement, tariff or other undertaking.
<PAGE>
 
9.       FORCE MAJEURE

9.1      Except for payment obligations,  neither Party shall be liable for
         failure to perform under this  Agreement due to any act,  event or
         cause  beyond  its  reasonable  control  ("Force  Majeure  Event")
         including, but not limited to:

         Acts of God,  peril  of the  sea,  accident  of  navigation,  war,
         sabotage, riot, insurrection,  civil commotion, national emergency
         (whether in fact or by law), martial law, fire, lightning,  flood,
         cyclone,  earthquake,  landslide,  storm or other adverse  weather
         conditions,  explosion,  power  shortage,  strike  or other  labor
         difficulty (whether or not involving COMSAT employees),  epidemic,
         quarantine, radiation or radioactive contamination;

         Action or inaction of any government or other competent authority,
         (including  any  court  of  competent   jurisdiction),   including
         expropriation,  restraint, prohibition, intervention, requisition,
         requirement,  direction  or  embargo  by  legislation  regulation,
         decree or other legally enforceable order; and Breakdown of plant,
         machinery   or   equipment,    externally   caused    transmission
         interference or satellite failure,  or satellite launch failure or
         delay,   or   satellite   malfunction,   or  shortages  of  labor,
         transportation,  fuel,  power or plant,  machinery,  equipment  or
         material.

9.2      In the  event  that a Force  Majeure  Event  exceeds  thirty  (30)
         consecutive  days,  then following  such  thirty-day  period,  the
         Parties  shall meet and negotiate  the  continuation,  suspension,
         termination, restructuring or other disposition of this Agreement.
         Upon  removal  or  cessation  of  the  Force  Majeure  Event,  all
         obligations under this Agreement shall resume,  unless the Parties
         determine to terminate or restructure the Agreement.

10.      ASSIGNMENT

         This  Agreement  shall not be  assigned or  transferred  by either
         Party without the prior written consent of the other Party,  which
         consent   shall  not  be   unreasonably   withheld   or   delayed.
         Notwithstanding  the  foregoing,  either  Party may,  without  the
         other's  consent,  make an assignment  to a successor,  affiliate,
         subsidiary, or to any entity controlling or under the same control
         as such a Party.

11.      GOVERNMENT APPROVALS

11.1     All agreements covenants, undertakings and obligations herein made
         or assumed by the Parties  hereto are subject to the  obtaining of
         all   necessary   governmental   licenses,    consents,   permits,
         authorizations,   and  approvals.  Each  Party  shall  obtain  and
         continue   to   maintain   such   licenses,   consents,   permits,
         authorizations, and approvals.

11.2     Both Parties  represent and warrant that they have been authorized
         as common  carriers  by the FCC  pursuant  to  Section  214 of the
         Communication  Act of 1934, as amended.  A copy of this  Agreement
         shall be filed with the FCC  pursuant  to Section  211 of such Act
         and shall seek confidential treatment of such filing.

12.      CONFIDENTIALITY

12.1     The  Parties  hereby  agree  that  it  may  be  necessary  to  the
         performance of this Agreement for a Party (the "Disclosing Party")
         to  disclose to the other Party (the  "Receiving  Party")  certain
         information   that  each  Party  deems  to  be  confidential   and
         proprietary.  The Receiving  Party shall maintain the security and
         confidentiality of all Confidential  Information received from the
         Disclosing Party hereunder.

12.2     For purposes  hereof,  "Confidential  Information"  shall  include
         business  and  technical  information  or  data  relating  to  the
         Disclosing  Party  and  its  representatives  that is  reduced  to
         writing  and  marked   "Confidential"  by  the  Disclosing  party.
         Notwithstanding   anything   contained  herein  to  the  contrary,
         Confidential   Information   shall  not  include  (i)  information
         developed   independently  by  the  Receiving  Party  or  lawfully
         received   from  a  third  party  not  under  an   obligation   of
         confidentiality;  or (ii)  information  in the public  domain;  or
         (iii)  information known by Receiving Party prior to the execution
         of this Agreement;  or information disclosed pursuant to law; (iv)
         judicial order or governmental regulation.
<PAGE>
 
12.3     The  Receiving  Party shall not use nor  communicate,  directly or
         indirectly, any of the Confidential Information to any third party
         without the prior written  consent of the  Disclosing  Party.  The
         Receiving Party shall use its best efforts to prevent  inadvertent
         disclosure of all or any part of the  Confidential  Information to
         any third party.

12.4     The  Receiving  Party's   obligations  under  this  Article  shall
         continue  for a period of two (2) years after the  termination  or
         expiration  of  this  Agreement  with  respect  to  each  item  of
         Confidential Information disclosed hereunder. Upon such expiration
         or  termination,  the Receiving  Party shall return or destroy all
         Confidential Information of the other Party in its possession.

13.      INTELLECTUAL PROPERTY  RIGHTS

         The   Parties   agree  that   trademarks,   inventions,   patents,
         copyrights, registered designs, service marks, trade names and all
         other  intellectual  property shall remain in the ownership of the
         person or party  originating  the same and  nothing  herein  shall
         confer or be deemed to confer on either Party  expressly,  implied
         or otherwise,  any rights or licenses in the intellectual property
         of the other.

14.      AMENDMENT

         This Agreement together with all Attachments and Exhibits,  may be
         amended, modified or amplified only by written agreement signed by
         authorized representatives of both Parties.

15.      WAIVER OF TERMS

         No waiver by either Party of any provision of this Agreement shall
         be binding unless  expressly  confirmed in writing.  Further,  any
         such  waiver  shall  relate  only  to  such   particular   matter,
         non-compliance  or breach as it expressly relates to and shall not
         apply to any subsequent or other matter, non-compliance or breach.

16.      GOVERNING LAW AND FORUM

16.1     The  existence,  validity,  construction,  operation and effect of
         this  Agreement  shall be  determined  in  accordance  with and be
         governed by the laws of the State of New York.

16.2     Any  dispute  arising out of or related to this  Agreement,  which
         cannot  be  resolved  by  negotiation   within  thirty  (30)  days
         following the date on which  written  notice of a dispute has been
         given to the other Party, shall be settled by binding  arbitration
         in accordance with the  J.A.M.S./ENDISPUTE  Arbitration  Rules and
         Procedures,  as amended by this  Agreement.  The number of neutral
         arbitrators  shall be three (3), one appointed by each Party,  and
         the third  appointed  by the other two  arbitrators.  The place of
         arbitration  shall be Washington,  D.C. The costs or  arbitration,
         including  the  fees and  expenses  of the  arbitrators,  shall be
         shared  equally  by  the  parties  unless  the  arbitration  award
         provides  otherwise.  Each party shall bear the cost of  preparing
         and presenting its case. The parties agree that this provision and
         the arbitrator's authority to grant relief shall be subject to the
         United States  Arbitration Act, 9 U.S.C. 1-16 et seq. ("USAA") and
         the provisions of this  Agreement.  The  arbitrators  shall comply
         with the  ABA-AAA  Code of Ethics for  Arbitrators  in  Commercial
         Disputes.  The parties  agree that the  arbitrators  shall have no
         power or  authority  to make  awards  or issue  orders of any kind
         except as expressly  permitted by this Agreement,  and in no event
         shall the  arbitrators  have the  authority to make any award that
         provides  for  punitive or  exemplary  damages.  The  arbitrators'
         decision  shall be final and  binding.  The award may be confirmed
         and  enforced  in  any  court  of  competent   jurisdiction.   All
         post-award proceedings shall be government by the USAA.
<PAGE>
 
17.      NOTICES

17.1     All notices,  invoices  and other  communications  made  hereunder
         shall be given in  writing  and  shall be deemed to have been duly
         given and effective (i) upon receipt, if delivered in person or by
         telecopy,  with  confirmation;  or (ii) one (1) day after  deposit
         prepaid  with  a  U.S.  domestic  overnight  express  service  for
         domestic  delivery;  or (iii) three (3) days after  deposit in the
         United States mail,  certified,  postage  prepaid,  return receipt
         requested;  or (iv) five (5) days after  deposit with an overnight
         express service for international delivery service.

         Notices to COMSAT of a contractual nature shall be directed to the
         following address:

         COMSAT Mobile Communications
         6560 Rock Spring Drive
         Bethesda, Maryland 20817
         Attention:  Contracts Department
         Telephone Number:  (301) 214-3450
         Facsimile Number:  (301) 214-7113

         Notices to COMSAT  related to invoices  and  collections  shall be
         directed to the following addresses:

         COMSAT Mobile Communications
         6560 Rock Spring Drive
         Bethesda, Maryland  20817
         Attention: Revenue Accounting Department
         Telephone Number:  (301) 214-3000
         Facsimile Number:  (301) 214-7113

         Notices to MCI of a  contractual  nature  shall be directed to the
         following address:

         MCI International, Inc.           MCI Worldcom, Inc.
         2 International Drive             1717 Pennsylvania Avenue, N.W.
         Rye Brook, New York  10573        Washington, D.C.  20006
         Attention:                        Attention: International Commercial 
                                              Affairs Law and Public Policy
         Telephone Number:                            
         Facsimile Number:                 Facsimile Number:  (202) 721-2549

         Notices  to MCI  related  to  invoices  and  collections  shall be
         directed to the following address:

         MCI International, Inc.
         2 International Drive
         Rye Brook, New York  10573
         Attention:
         Telephone Number:
         Facsimile Number:

18.      MISCELLANEOUS

18.1     No Third Party  Beneficiary.  The provisions of this Agreement are
         for the benefit only of the Parties hereto, and no third party may
         seek to enforce or benefit from those provisions.

18.2     No Partnership Or Agency  Relationship.  The relationship  between
         COMSAT  and MCI  shall  not be that of  partners  or agents of one
         another,  and nothing  contained in this Agreement shall be deemed
         to constitute a partnership or agency agreement between them.
<PAGE>
 
18.3     Successors and Assigns.  This Agreement shall be binding upon and 
         inure to the benefit of each Party's successors and permitted 
         assignees.

18.4     Headings.  The titles in the headings of  paragraphs  are intended
         for  organization  and  convenience  only and do not  apply in the
         interpretation of any of the Agreement terms.

18.5     Survival  of Terms.  The terms and  provisions  contained  in this
         Agreement  that by their sense and context are intended to survive
         the performance thereof by the Parties hereto shall so survive the
         completion of

18.6     Rule  of   Construction.   No  rule  of   construction   requiring
         interpretation  against the  drafting  party hereof shall apply in
         the interpretation of this Agreement.

19.      ENTIRE AGREEMENT

         This Agreement,  together with all attachments incorporated herein
         specifically by reference,  represents the entire understanding of
         the  Parties  with  respect to the subject  matter  hereof and all
         other agreements (written or oral) between the Parties relating to
         the Service shall be superseded by this Agreement.

20.      SEVERABILITY

         If any one or more of the  provisions  contained in this Agreement
         or any document executed in connection  herewith shall be invalid,
         illegal or  unenforceable in any respect under any applicable law,
         the  validity,   legality  and  enforceability  of  the  remaining
         provisions  contained  herein  shall not in any way be affected or
         impaired;  provided,  however, that in such case the Parties agree
         to use their best  efforts to achieve  the  purpose of the invalid
         provision by a new legally valid stipulation.

 21.     SUPERSEDES OTHER AGREEMENTS

         This Agreement  specifically  supersedes and cancels the Agreement
         dated  1  September   1993,   entered   into  by  COMSAT  and  MCI
         International,  Inc.,  which  Agreement  shall be null  and  void,
         except for any  liabilities  of the Parties that arise  thereunder
         prior  to  the  date  of  such   cancellation   and  which  remain
         outstanding.


IN WITNESS  WHEREOF,  the Parties  hereto have executed  this  Agreement in
counterparts on the day and year first above written.

COMSAT Mobile Communications,                  MCI International, Inc.
a business unit of COMSAT Corporation

/s/ Carol M. Schoonhoven                       /s/ Anthony Cirieco
CAROL M. SCHOONHOVEN                           ANTHONY CIRIECO
20 NOVEMBER 1998                               11/6/98